Commonly known as "identical twins" monozygotic
twins are from a single egg that has divided after fertilization to create two embryos.
Monozygotic twins consequently share exactly the same genetic material and are of the same
Monozygotic twins who have been separated in earliest
infancy and raised apart have provided a classic research situation for social scientists
because their genetic identity, yet different social experience, makes it possible to
disentangle the separate effects of heredity and social environment.
The ban on human cloning in many countries worldwide is
founded on an assumption that cloned children will be identical to each other and to their
How identical would cloned children be? An
understanding essential to the ethical debate - RG Edwards and HK
Beard, Human Reproduction Journals - This paper explores the scientific basis for
this assumption, considering both the principles and practice of cloning in animals and
comparing genetic and epigenetic variation in potential human clones with that in
Cognitive and Personality Differences Between
Identical Twins Following Skull Fractures - Michael J. Lyons and Adam P.
Matheny, The University of North Carolina at Charlotte, University of Louisville School of
Medicine, Journal of Pediatric Psychology 9(4) pp. 485-494, 1984 © 1984 Society of
The classical co-twin control method was used to evaluate the effects of age at the time
of skull fracture on behavioral functioning several years later. The sample consisted of
13 pairs of male monozygotic twins. One twin had suffered a noncompound skull fracture
during one of the following two periods: between 12 and 36 months of age (five pairs) or
between 36 and 48 months (eight pairs). All twins were given the Wechsler Preschool and
Primary Scale of Intelligence (WPPSI) at 6 years of age and their mothers rated the twins
on a personality/temperament scale. When compared with their co-twins, the twins injured
between 12 and 36 months had no cognitive deficits, but had higher scores on a factor
denoting ratings of emotionality.
Female Monozygotic Twins with Selective Mutism - A
Journal of Developmental & Behavioral Pediatrics. 27(2):129-133, April 2006.
SHARKEY, L. 1; MC NICHOLAS, F. 2
Abstract: Selective mutism is a rare social anxiety disorder characterized by a total lack
of speech in certain specific situations despite the ability to speak in others. Both
genetic and psychosocial factors are thought to be involved in its presentation,
persistence, and response to treatment. This case report describes a case of young female
monozygotic twins who presented with selective mutism and their treatment spanning a
2-year period. It highlights the strong genetic association along with environmental
factors such as social isolation and consequences of maternal social phobia, all
contributing to treatment resistance, despite an intensive multimodal biopsychosocial
approach. General issues related to the difficulties in treating monozygotic twins are
Monozygotic twins discordant for major depression: a preliminary exploration of
the role of environmental experiences in the aetiology and course of illness
KENNETH S. KENDLER and CHARLES O. GARDNER
Departments of Psychiatry and Human Genetics, Medical College of Virginia of Virginia
Commonwealth University and Virginia Institute for Psychiatric and Behavioral Genetics,
Richmond, VA, USA
Abstract: Background. Genetic effects upon behaviour are pervasive. To what extent are the
many correlates of major depression (MD) due to individual-specific environmental
experiences versus genetic factors correlated with risk for MD?
Methods. From a population-based twin registry, we identified 72 female monozygotic twin
pairs discordant for a lifetime history of MD and compared the affected and unaffected
members on a wide range of putative correlates of MD.
Environmental factors cause pervasive differences in monozygotic twins discordant for MD,
especially in the areas of interpersonal difficulties, psychopathology, social problems